Coordinate measuring machines (CMMs) are the gold standard for accurately measuring a wide variety of work pieces. For example, CMMs can measure critical dimensions of aircraft engine components, surgical tools, and gun barrels. Precise and accurate measurements help ensure that their underlying systems, such as an aircraft in the case of aircraft components, operate as specified.
Recently, those in the art have begun using computed tomography (CT) systems as CMMs for coordinate metrology. As known by those in the art, a CT system generates three-dimensional images of an object as a function of the attenuation of its x-rays by the object. Some materials, such as metal, may attenuate x-rays sufficiently under typical x-ray power settings, to generate an appropriate image. Other materials, however (e.g., polymers), may not sufficiently attenuate x-rays at the same or similar power settings.
This creates problems for heterogeneous objects. More specifically, CT imaging techniques known to the inventors do not adequately image objects made from heterogeneous materials in a way that is non-invasive or non-destructive. For example, those techniques cannot adequately image a stent, which is made from a metal mesh frame supporting one or more polymers. Although the metal mesh should adequately attenuate the x-rays, the polymer typically does not. Accordingly, rather than producing an image of the entire stent, the noted techniques may produce an image of the metal mesh without the polymers. Indeed, such an image does not have enough information to measure many of its important features, such as those features formed from polymers.